Back to EveryPatent.com
| United States Patent |
5,087,512
|
|
Uihlein
, et al.
|
February 11, 1992
|
Surface coating for protecting a component against titanium fire and
method for making the surface coating
Abstract
A structural component of metal is protected against titanium fires that
can be caused by flying and burning titanium droplets, e.g. in a
propulsion unit. The protection against titanium fires of metal structural
components is provided by a surface coating made of ceramic fibers
embedded in a matrix material of a high temperature lacquer having
dispersed therein aluminum powder as a filler material. The high
temperature resistant lacquer is formed of silicates as a vehicle in which
the aluminum powder is dispersed.
| Inventors:
|
Uihlein; Thomas (Karlsfeld, DE);
Wydra; Gerhard (Oberschleissheim, DE)
|
| Assignee:
|
MTU Motoren-und Turbinen-Union Muenchen GmbH (Munich, DE)
|
| Appl. No.:
|
625747 |
| Filed:
|
December 11, 1990 |
Foreign Application Priority Data
| Current U.S. Class: |
442/232; 428/183; 428/293.4; 428/328; 428/600; 428/631; 428/632 |
| Intern'l Class: |
B32B 015/04; B32B 033/00 |
| Field of Search: |
428/263,183,256,266,288
|
References Cited
U.S. Patent Documents
| 2858600 | Nov., 1958 | Vigor | 29/198.
|
| 3471342 | Oct., 1969 | Wood | 428/660.
|
| 4024303 | May., 1977 | Hahn | 427/295.
|
| 4137370 | Jan., 1979 | Fujishiro et al. | 428/660.
|
| 4238551 | Dec., 1990 | Lal et al. | 428/660.
|
| 4305998 | Dec., 1981 | Marty et al. | 428/661.
|
Primary Examiner: Lesmes; George F.
Assistant Examiner: Weisberger; Richard
Attorney, Agent or Firm: Fasse; W. G.
Claims
What we claim is:
1. A structural component made of metal to be protected against titanium
fire caused by a component of titanium or titanium alloy by a surface
coating comprising a matrix material including a mixture of at least one
silicate and aluminum powder dispersed in said silicate, and ceramic
fibers made of a material selected from the group consisting of silicon
oxide, aluminum oxide, zirconium oxide, and mixtures of the foregoing
oxides, said ceramic fibers being embedded in said matrix material to form
said surface coating against damage by molten titanium or titanium alloy
droplets protective coating.
2. The component of claim 1, wherein said ceramic fibers are arranged as
layers of said fibers.
3. The component of claim 1, wherein said ceramic fibers are arranged as a
fiber fabric or webbing.
4. The component of claim 1, wherein said matrix material comprises an
inorganic high temperature lacquer
5. The component of claim 1, wherein said protective coating has a density
within the range of 0.8 to 2.0 grams per cubic centimeter.
6. The component of claim 1, wherein said protective coating has a
thickness within the range of 0.5 to 20.0 mm.
7. The component of claim 6, wherein said thickness is within the range of
1.0 to 10.0 mm.
8. The component of claim 1, further comprising a gas-tight surface layer
on said protective coating.
9. The component of claim 8, wherein said gas-tight surface layer is a
silicate layer.
10. The component of claim 1, wherein said silicates of said matrix
material are selected from the group consisting of organo- or
metalsilicates.
11. The component of claim 1, wherein said aluminum powder in said matrix
material has a powder particle size within the range of 3 .mu.m to 40
.mu.m.
12. The component of claim 1, wherein said aluminum powder is present in
said matrix material within the range of 30 wt. % to 60 wt. %. of said
matrix material.
Description
FIELD OF THE INVENTION
The invention relates to a protective surface coating on a structural
component made of metal. Such metal components can be set on fire or at
least damaged on the surface by a so-called titanium fire that can be
caused by molten titanium droplets, for example, in a turbine. The
protective coating is made of ceramic fibers embedded in a matrix
material.
BACKGROUND INFORMATION
A spontaneous ignition of titanium is possible at temperatures above
500.degree. C. in an oxidizing atmosphere. The resulting fire in the form
of spraying molten titanium droplets endangers and impairs the possible
utilization of this material at higher operating temperatures. German
Patent Publication 3,906,187, corresponding to U.S. Ser. No. 07/485,044,
filed on Feb. 26, 1990, discloses a solid or compact coating for
components subject to titanium fires which bring such fires under control.
However, the drawback of such conventional coatings is their limited
thickness, which is easily penetrated by molten titanium droplets having a
high kinetic energy when high intensity titanium fires occur. The
penetrated surfaces of the structural metal are then subjected to
oxidizing attack. Besides, the density of the known coatings makes the
coating rather heavy. Further, the known coatings have a low thermal
insulation or low R-factor.
German Patent Publication (DE-AS) 1,947,904 discloses a fiber composite
material of aluminum silicate fibers in a silicon dioxide matrix including
aluminum or silicon particles and, preferably, a filler of coke or
aluminum dioxide. The just mentioned publication also describes a method
for the manufacture of the fiber composite material. The known fiber
composite material has the drawback that the arrangement of the fibers,
due to the described manufacturing process from an aqueous sludge, tends
to be irregular and haphazard. Unavoidable local concentration or thinning
of fibers leads to disadvantageous nonuniformities in the fiber composite
material and weaken its protective effect. The silicon dioxide matrix made
from silicic acid has the further disadvantage of high temperature
embrittlement due to Christobalit formation. Hence, the known material is
not suitable for continuous loading in the hot gas flow of, for example, a
gas turbine engine.
OBJECTS OF THE INVENTION
In view of the above it is the aim of the invention to achieve the
following objects singly or in combination:
to provide a protective coating for a metal structural component, which
coating will effectively protect the component against damage by titanium
fires;
to provide a method for the manufacture of the protective coating;
to effectively check or control a titanium fire that causes molten titanium
droplets having a high kinetic energy;
to protect the surfaces of the structural component against heat damage and
titanium melt attack; and
to generally contain titanium fires from spreading.
SUMMARY OF THE INVENTION
According to the invention a coating is made of ceramic fibers of
SiO.sub.2, Al.sub.2 O.sub.3, ZrO.sub.2 or of mixtures of said oxides are
arranged in layers or as a web or webs and embedded in a matrix material
made of silicates having embedded in the matrix material aluminum powder
as a filler. The silicates are selected from the groups of organo- or
metalsilicates according to U.S. application Ser. No. 07/485,044, whereby
silicates of alkyl, sodium, potassium, aluminum, or zinc are preferred.
The advantage of such a coating on a structural component, is that the
kinetic energy of the molten titanium droplets is absorbed by the
fiber-matrix-structure of the coating and the thermal energy of the
titanium melt is used up in the melting of the aluminum powder embedded in
the matrix of the coating. Further, the high thermal insulation property
of the ceramic fibers in a silicate matrix prevents overheating of the
surface of the structural component to be protected. The arrangement of
the ceramic fibers in this protection coating against titanium fires in
layers or as a web or fabric advantageously creates a homogenous fiber net
which avoids the uneven distribution of the previously known fiber
arrangements. The present coating also has a higher resistance against
erosion than conventional coatings.
Preferably, the matrix is formed of an inorganic high temperature lacquer
which has the advantage of a simultaneous adhesive bonding action and
embedding to hold the protective mat to the surface of the metal
structure. This feature obviates the need for a partial fastening of the
ceramic fibers by sintering, soldering, or welding to the structural
component surface which is to be protected.
Component surfaces coated in accordance with the invention are preferably
used in gas turbines for aviation engines. For this purpose a preferred
protective coating of the invention has a density within the range of 0.8
to 2.0 g/cm.sup.3. This low density has the advantage that a relatively
thick protection coating, in comparison to conventional denser coatings,
can be used without a weight increase, so that the kinetic energy of
molten titanium droplets can be absorbed by the present coating.
Protection coatings according to the invention have a thickness within the
range of 0.5 to 20 mm. preferably from 1 to 10 mm. The preferred range
covers protective coatings for most purposes while the extended range
advantageously also permits extremely thin and relatively thick coatings
for special purposes. The thin range of 0.5 to 1.0 mm competes with
compact or dense conventional coatings with the added advantage that the
present coatings are permeated by thermally insulating ceramic fibers,
while dense conventional coatings do not provide a useful heat insulation.
The thickness range from 10 to 20 mm provides solutions to titanium fire
protection problems that heretofore could not be realized.
The sealing of the surface of the coating advantageously provides a
nonporous, gas-tight cover for the structural component in combination
with the protection against titanium fire, so that penetration and
inflation of the fabric by an oxidizing gas flow is prevented.
The method for manufacturing the present coating on a structural component
for protection against a titanium fire, is performed as follows:
(a) drying or heating of the ceramic fibers of a ceramic fiber material in
the form of layers or webbings or fabrics to clean the surface of the
fibers;
(b) infiltration or impregnating of the ceramic fiber material with
silicates, selected from the above mentioned group, whereby alkyl
silicates, sodium silicates, potassium silicates, and mixtures of the
foregoing silicates are preferred,
(c) application of an inorganic high temperature lacquer of a silicate
binder and an aluminum powder dispersed in the silicate binder, wherein
the aluminum powder forms a filler, to the surface of the structural
component and to the surface of the ceramic fibers,
(d) placing said infiltrated or impregnated fiber material on said coated
surface of said structural component.
(e) coating and infiltrating said fiber material with said high temperature
inorganic lacquer of a silicate binder and an aluminum powder dispersed as
a filler in said silicate binder.
(f) drying or burning-in of the high temperature lacquer, and
(g) sealing of the surface of the protective coating with silicates also
from the above group. The silicate binder of step (c) is selected from the
group of organo- or metalsilicates.
The advantage of the present method is that a cost and functionally
effective protection against titanium fire is provided with commercially
available means. The protection simultaneously reduces the thermal loading
of the structural component because of the heat insulating properties of
the ceramic fibers and of the silicates.
The drying or heating of the fibers of the ceramic material in the form of
layers, webbings, or fabrics cleans the ceramic fibers, so that the
subsequent infiltration or embedding of silicates fully penetrates the
fabric and wets the surface of the fibers. The above mentioned silicates
may be used singly or in any combination of the silicates listed.
The application of an inorganic high temperature lacquer with aluminum
filler to the surface of the structural component greatly improves the
bonding of the coating to the component surface. After placing the
infiltrated fiber material onto the lacquered component, the surface of
the fiber material is again brush painted, sprayed, or spattered, so that
the following drying and burning-in process forms a protective coating
made of ceramic fibers of SiO.sub.2, Al.sub.2 O.sub.3, ZrO.sub.2, or
mixtures thereof, whereby the fibers are embedded in the matrix material
containing silicates with aluminum powder embedded in the silicates.
The surface of the protective coating often has open pores, and is wavy and
uneven. Therefore, the surface is afterwards sealed in such a way with
silicates that it becomes gas-tight and smooth. The silicates are selected
from the above group.
To make protective coatings of greater thickness another, or even several,
applications of fiber material and an inorganic high temperature lacquer
are applied to the unsealed surface so that protective coatings of
thickness up to 20 mm can be manufactured.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the invention may be clearly understood, it will now be
described, by way of example, with reference to the single Figure
illustrating an example embodiment and a manufacturing method, whereby the
Figure shows the construction of a metal structural component coated on
its surface with a protection against titanium fire.
DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE BEST MODE
OF THE INVENTION
The figure shows the construction of a structural component 1 of metal, for
example steel, with a protective coating 4 which firmly adheres to the
surface 5 of the structural component 1. The adhesion is due to the
inorganic high temperature lacquer which forms, together with silicates as
binder and aluminum powder as filler, a matrix material 2 of the
protective coating 4. Ceramic fibers are embedded in the matrix material 2
which contains ceramic fibers 3a, 3b, 3c of SiO.sub.2 /Al.sub.2 O.sub.3
arranged, for example, in three plies. In the figure one fiber 3b is shown
to extend longitudinally. However, there are more than one longitudinally
extending fibers 3b to form an intermediate fiber ply. A plurality of
cross-sectioned fibers 3a, 3c form two further plies. These fiber plies
may be interwoven with each other to form a fabric, or they may simply
form non-interwoven plies or layers. The surface 6, is sealed by silicates
to protect the coating against penetration by hot oxidizing gases which
hit the surface 6 of the protective coating in the direction of arrows 7.
The structural component of metal with the protective coating against
titanium fire secured to the component surface as shown in the figure was
made as follows. First, the surface of the structural component 1 was
cleaned and a silicate binder was applied to the surface. After drying of
the silicate binder, an inorganic high temperature lacquer with aluminum
powder as filler was applied. The three layers or plies 3a, 3b, 3c of
fiber material of SiO.sub.2 /Al.sub.2 O.sub.3 were first dried and heated
to a glow, so that the fiber surfaces were completely free of
contaminations.
The three layers or plies of fibers 3a, 3b, 3c were then soaked in
silicate, dried, and applied to the surface of the structural component
still sticky by the high temperature inorganic lacquer. High temperature
lacquer with a filler of aluminum powder, was then sprayed on the fiber
layer. Afterwards, the lacquer was dried and baked to a 1 mm thick
protective coating on the surface 5 of the structural member 1.
Finally, the surface of the protective coating was sprayed with silicate
and heated for the baking or burning-in of the silicate to form a
gas-tight seal to protect the protective coating itself against gas and
contamination intrusion. The density of the coating in this example is 1.5
g/cm.sup.3.
Top